Field of the Invention
The invention relates to an arc evaporation source used in an arc ion plating device.
Description of Related Art
For film formation of a ceramic hard film on a substrate, conventionally, an arc ion plating method using an arc ion plating device for evaporating and ionizing a cathode material of an arc evaporation source by arc discharge in a vacuum is commonly used for film formation on a surface of the substrate (work) (for example, patent documents 1 and 2).
An example of the arc evaporation source used in this type of arc ion plating method is illustrated in FIG. 24. Referring to FIG. 24, the arc evaporation source is constructed by a cathode 1 machined in a disc shape and fixed by a fixing ring 2, and a permanent magnet 4 disposed on a side of the cathode 1 that is opposite to the side of the discharge surface such that the direction of the magnetic poles is oriented along the axis direction of the cathode 1. In addition, 3 denotes one of the magnetic lines emitted by the permanent magnet 4.
Arc spots are formed on the discharge surface of the cathode 1 sequentially by arc discharge such that the cathode material evaporates; however, the arc spots have a tendency to move in an acute angle direction relative to the magnetic field.
Therefore, in FIG. 24, in addition to disposing the magnet 4 at a back side of the cathode 1, a part near the outer circumference of the cathode 1 is machined in a bank shape, so as to control the arc state. By using this type of cathode, the magnetic line 3 emitted by the magnet 4 is formed so as to spread outward in the radius direction of the cathode, and in addition the arc spots are prevented from escaping out of the discharge surface of the cathode. However, since the discharge area is mainly concentrated near the outer circumference on the inner side of the bank, as the number of batches of film formation increases, the shape of the cathode 1 changes from the shape illustrated by the dotted line in FIG. 25 to the shape illustrated by the solid line, such that the cathode material is not able to be effectively used up to the center portion of the discharge surface.
In addition, as shown in FIG. 26, instead of machining the part near the outer circumference of the cathode 1 into a bank shape, techniques have been proposed to construct the arc evaporation source so as to include a tapered confinement ring 5 at the outer circumference of the cathode 1, such that arc spots are prevented from escaping.
However, in this case, since the outer circumference of the cathode 1 is covered by the confinement ring 5, the outer circumference of the discharge surface is not able to be used to the fullest and interferes with the effective utilization of the cathode material.
That is to say, as shown in FIGS. 27(a) and (b), cathode materials having the same area (the hatching portion of the figure) as viewed from the cross section view are used, however in 3-dimensional terms the volume of the cathode material utilized may be represented by,V2=V1×(D2÷D1)and since D2>D1, it may be seen that the outer circumference may be used to the fullest and a larger volume of the cathode material may be used, so as to be utilized effectively.